Color Measurement
and Analysis
CT&A ISO 3664+ TOOLS
color monitors
This tool is based on the "Color monitors" viewing condition defined in ISO 3664:2009 and incorporates selected requirements of
ISO 12646:2008 and ISO 12646:2014 (ISO 3664+ specifications):
•
Brightness
•
Chromaticity (u'v')
•
Correlated Color Temperature (CCT), in kelvin
•
Color Rendering Index (CRI)
•
Daylight simulator Metamerism Index (MI) and Quality Grade (visible-range-only)
•
Brightness uniformity as per ISO 12646:2008, Section 4.4: The relative brightness of WHITE, GREY, and DARK-GREY targets can be
measured on a non-uniform 3 x 3 grid which favors the monitor's center area.
•
Tone uniformity, i.e. Color uniformity, as per ISO 12646:2014-Final Draft, Section 4.2.2: Measurements can be done on WHITE, GREY,
and DARK-GREY targets positioned on a uniform 5 x 5 grid.
•
Tonality Evaluation, i.e. Grey/White Tone ratio uniformity, as per ISO 12646:2014-Final Draft, Section 4.2.3: Measurements can be
performed for up to twenty-five positions located on a uniform 5 x 5 grid.
In the screenshot above, we have measured a white target at the twenty-five positions of a 5 x 5 grid defined by ISO 12646:2014. The center
position is selected and its brightness and chromaticity easily pass the requirements of ISO 3664 (126 cd/m2 with a chromaticity offset is
0,001); this display had just been calibrated (in the center!) for a nominal 120 cd/m2 at D65. However, we can see that the Color uniformity test
fails, with color differences (computed using CIEDE2000) relative to the center position exceeding the limit of 4. By selecting another position,
you could see this other position's absolute "Brightness", "Meas. Temp." (Color temperature) and "Meas. offset" (chromaticity offset).
For each position you can see three smaller squares with a center colored Dark-Grey (Dk-Gy), Grey, and White respectively. In the screenshot,
all White squares have a green border, indicating they were measured, and the Dark-Grey and Grey squares have a yellow border, indicating
there are not measured. We could select the Grey or Dark-Grey radio button on the right and then proceed to complete the measurements.
We could also save all test data in a file by clicking on the "Save to file..." button. You will find a more
detailed presentation in Tutorial 8 of the CT&A Help manual (The Help manual is available in the
downloadable program file or as a separate pdf file).
The CHROMATICITY target is a very useful tool in its own. You can select the target center amongst
several standard Illuminants, including 3200 K, a color temperature often used for TV Studio lighting.
You will notice three colored diamonds around the target; these diamonds identify primary colors that
need to be removed, when you are close, or added, when you are far, in order to approach the target
center (these primaries are in reference to the CIE1976 x'y' Chromaticity diagram obtained with the 10
degree Observer). When these diamonds are used in conjunction with the Tuning Mode, engaged by
clicking on the "Tune" button, and which automatically triggers the i1Pro or i1Pro 2 at fixed time
intervals, you obtain a powerful tool to adjust a display White Point. The Tuning Mode can be used with
the other Viewing Conditions as well.
You can obtain a global snapshot of the test results by printing a one page report, shown below, which is
useful for compliance-type reporting. This report includes the measurements done with the Grey and
Dark-Grey targets. For this monitor, according to our measurements, the min. luminance and max. CCT
is in the upper-left while the max. luminance and min. CCT is in the bottom-right; these variations
correlate well with the Color uniformity results but while the luminance and chromaticity are within
requirements, the Color uniformity fails for all target colors. A similar report is available for all viewing
conditions
These tools are called ISO 3664 with a "+" to indicate that alternate reference illuminants can be selected by the user for each test. For
example, while ISO 3664 calls for a D65 target center for monitors, many would prefer using a D50 target, as recommended in ISO 12646
(Graphic technology -- Displays for colour proofing -- Characteristics and viewing conditions); to do so, simply select D50 in the "Target center"
popup menu.
In our example, we selected D65 as the chromaticity target center because this was the white point used to calibrate our display. We used the
"Take all" button to rapidly measure all the targets of a given color, which are displayed one by one at the specified locations if you are doing
the measurements on the same computer on
which CT&A is running.
You can also open an image of the targets and
measure them manually; this is helpful when you
want to measure the characteristics of a monitor
not connected to the computer on which CT&A is
installed. To facilitate this task, we provide a built-
in dialog to create image files of targets for any
display size. Separate files are generated for the
White, Grey, and Dark-Grey target patches. File
formats: PNG or TIFF; RGB; 8-bit. Shown below, in
reduced size, is an image with white targets
positioned as per ISO 12646:2014 (5x5 grid).
The data associated to the fields circled in red can be assigned with a
dialog which opens when you click on the “Print report…” button.